JP2000081322A - Slip angle measuring method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine a slip angle. SOLUTION: Images of a road surface taken by CCD cameras 14a-14d mounted on wheels 12a-12d are recorded into a VTR device 20. A slip angle calculator 24 determines a slip angle from the image of the road surface. The flow of the road surface appears on the image of the road surface during the exposure period of the cameras. The slip angle is determined from the direction of the flow of the road surface. The use of a lighter solid sate image sensing device such as CCD permits accurate determination of the slip angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring a vehicle slip angle using an image measurement technique.

[0002]

2. Description of the Related Art As is well known, in vehicle development, a slip angle is measured and used as a parameter representing vehicle behavior. The slip angle is, for example, a tire slip angle and a vehicle body slip angle, and is an angle indicating a direction in which the tire and the vehicle body move with respect to a road surface, respectively. Here, we will mainly focus on the tire slip angle.
The invention is not limited to measuring tire slip angles.

Referring to FIG. 1, the X direction is the direction of the rotation axis of the tire, the Y direction is the direction in which the tire rolls,
x and Vy are the speeds at which the tire moves in the X and Y directions, respectively. The tire slip angle θ is θ = tan ⁻¹ (Vx /
Vy). The tire slip angle is used for tire testing, development of a vehicle stabilization device, and the like. The vehicle stabilizing device is a device that suppresses a turning moment of a vehicle body to stabilize a vehicle behavior.

[0004] As the slip angle measuring device, an ultrasonic type and a photodiode type are known. For example, Japanese Unexamined Patent Publication No. Hei 8-183434 discloses an ultrasonic type measuring device.

[0005]

When a conventional commercial slip angle meter is used, a relatively heavy measuring unit (for example, about 3 kg) must be generally mounted on the wheel, which means that the measuring accuracy is low. It is a problem from the point of view. Increasing the unit weight increases the unsprung vehicle weight, which can result in unsprung movements that would not otherwise occur, which could result in different vehicle movements when the unit is installed and when it is not installed. Because it is expensive. This can be a fatal drawback when using a slip angle meter as a measuring device.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a new measuring method and apparatus capable of detecting a slip angle with high accuracy.

[0007]

The slip angle measuring method according to the present invention is characterized in that a road surface image is photographed while traveling using a camera mounted on a vehicle, and a slip angle is obtained from the road surface image. The road surface image can be taken using, for example, a lightweight camera having a solid-state imaging device. The road surface image may be guided to the camera using a transmission means such as an optical fiber.

When a road surface is photographed, the vehicle moves during the camera exposure time, so that the road surface image cannot capture a fine pattern of the road surface. The road surface image reflects the flow of the road surface during the camera exposure time like a so-called blurred image. By utilizing this, the slip angle can be obtained from the flow direction of the road surface in the road surface image. Thus, the present invention provides
Since the slip angle is obtained from the blurred road surface image, there is an advantage that the slip angle can be measured with a small cost using a standard camera.

Preferably, a plurality of patterns similar to each other are searched for from the road surface image, and the flow direction of the road surface is determined from the positions of the plurality of patterns. Since patterns similar to each other exist at positions shifted along the flow direction of the road surface, the flow direction of the road surface can be determined from the positional relationship between those patterns. By such processing, the flow direction on the road surface can be accurately obtained.

The present invention is applicable to measuring tire slip angles, vehicle body slip angles and any other slip angles. For example, a tire slip angle can be obtained from a road surface image viewed from a wheel. Further, the vehicle body slip angle can be obtained from a road surface image viewed from the vehicle body. Further, a tire slip angle can be obtained from a road surface image viewed from the vehicle body and a wheel steering angle.

Another aspect of the present invention is a slip angle measuring device, which is mounted on a vehicle, and that has a photographing means for photographing a road surface image while the vehicle is running, and a slip angle from a road surface image photographed by the photographing means. Means for calculating a slip angle to be obtained.

As described above, according to the present invention, the slip angle is obtained from the road surface image. Since the road surface image can be acquired using a lightweight solid-state imaging device or the like, the influence of the weight of the measuring device on the measurement data can be reduced. Thereby, the slip angle can be accurately detected.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter, embodiments) will be described below with reference to the drawings. In the present embodiment, the present invention is applied to measurement of a tire slip angle.

FIG. 2 shows a slip angle measuring device according to the present embodiment. CCD cameras (charge-coupled device cameras) 14 are attached to four wheels 12a to 12d of a vehicle 10, respectively.
a to 14d are attached. Here, FR in the figure
Denotes a front right wheel, FL denotes a front left wheel, RR denotes a rear right wheel, and RL denotes a rear left wheel.

Referring to FIG. 3, the CCD camera 14 is mounted on a camera mounting jig 50, and the mounting jig 50 is mounted on the wheels 12. The mounting jig 50 has a rotating member 52 and a non-rotating member 54. The rotating member 52 rotates together with the wheel 56. The non-rotating member 54 is attached to the rotating member 52 via a rolling bearing 58, and is connected to the vehicle body via a link 60. Therefore, the non-rotating member 54 changes its direction integrally with the wheel 12, but does not rotate with the wheel 12. CC
The D camera 14 is fixed downward to the non-rotating member 54 and changes its direction together with the non-rotating member 54.

Returning to FIG. 2, the CCD cameras 14a to 14d
Are the camera control units 16a-1
Under the control of 6d, the lower road surface is photographed while the vehicle 10 is actually traveling. The analog video signal of the road surface image is transmitted to the multiviewer 1 from the camera control units 16a to 16d.
8 is output. The multiviewer 18 has a screen synthesizing function and synthesizes four video signals to generate a 4-split screen as shown in FIG. The composite road surface image is output from the multiviewer 18 to the VTR device 20 and recorded.
The road surface image is photographed at a predetermined photographing cycle (for example, 1/60 second)
And one synthetic road surface image is generated and recorded in each photographing cycle.

A video tape on which a road surface image is recorded is a VT
It is removed from the R device 20, taken out of the vehicle, and set in the image processing device 22 outside the vehicle. Image processing device 22
Converts the analog video signal of the road surface image into a digital signal and outputs the digital signal to the slip angle calculation device 24. Here, conversion from an original black-and-white image to a 256-level grayscale digital image is performed. The slip angle calculation device 24 is a device in which a slip angle calculation program is incorporated in an ordinary personal computer or a workstation. The slip angle calculation program is a program that calculates a slip angle from a road surface image according to a slip angle calculation algorithm described below.

Referring to FIG. 4 again, the road surface image of each wheel is obtained by one photographing, and corresponds to one field (or one frame) of a moving image or a still image. The road surface moves by a distance corresponding to the vehicle speed during the camera exposure time. Therefore, a road surface pattern, for example, a granular fine pattern is not clearly photographed. Instead, the road surface image becomes a so-called “blurred image”. However, since the road surface moves in a substantially constant direction during the short exposure time, the flow of the road surface appears as a stripe pattern in the "blurred image". If the direction of the striped pattern is determined as the direction of flow on the road surface, the slip angle at the time of shooting can be calculated.

The exposure time of the CCD camera 14 is adjusted and set so that the flow on the road surface appropriately appears on the road surface image. If the exposure time is too long or too short, it becomes difficult to grasp the state of the flow on the road surface. The length of the exposure time is determined by the shutter speed of the electronic shutter or the mechanical shutter of the CCD camera 14. CC
The D camera 14 captures an image of the road surface at the shutter speed specified by the camera control unit 16.

Preferably, the exposure time (shutter speed) is adjusted according to the vehicle speed at the time of photographing. This is because the road surface flows at a speed corresponding to the vehicle speed. When the vehicle speed is high,
The exposure time is set short, and when the vehicle speed is low, the exposure time is lengthened. As a result, the flow state on the road surface is satisfactorily photographed at an arbitrary vehicle speed. For example, when the vehicle is traveling at 55 km / h, if the exposure time is set to 1/125 second, the road surface flows about 122 mm in the frame, and
As a result, a striped image as shown in FIG.

Next, a specific slip angle calculating process of the present embodiment will be described with reference to FIG. FIG. 5A shows FIG.
Is a quarter of the combined road surface image. Road surface images include
The x-axis is set in the horizontal direction and the y-axis is set in the vertical direction based on the pixel. The center point of the image is (Xi, Yi). A reference pattern having an area of a predetermined shape centered on the center point (Xi, Yi) is set. In addition, the center point (X
A rectangular search area centered on (i, Yi) is set. The coordinates of the four corners of the search area are (Xmi
n, Ymin), (Xmax, Ymin), (Xmi
n, Ymax) and (Xmax, Ymax). In the following manner, a pattern similar to the reference pattern is searched from the search area.

As shown in FIG. 5B, first, a comparison target pattern centered on the end point (Xmin, Ymin) of the search area is compared with the reference pattern. Here, a pattern matching process using a well-known normalized correlation method is performed, and the similarity between the two patterns is obtained. The pattern to be compared is shifted by one pixel in the x direction, the matching process is performed again, and the similarity is obtained. The same processing is repeated until the center point of the comparison target pattern reaches (Xmax, Ymin). Then, the largest similar pattern having the largest similarity is selected from all the patterns to be compared, and its center point (X1, Y1) is detected and recorded (FIG. 5C).

Next, the same processing as described above is performed for the y coordinate which is larger than Ymin by a predetermined number ys. The pattern matching is performed while shifting the center point of the comparison pattern from (Xmin, Ymin + ys) to (Xmax, Ymin + ys) by one pixel. The center point of the largest similar pattern is detected and recorded.

The same processing is repeated while moving the comparative pattern stepwise downward by a predetermined number ys.
The center point of the maximum similar pattern is sequentially obtained and recorded. Almost the same pattern should be lined up in the flow direction on the road surface. Therefore, as a result of the above processing, as shown in FIG. 5D, the maximum similar pattern center points arranged at substantially equal intervals along the road surface flow direction are obtained. The first obtained center point is (X1, Y1), and the j-th obtained center point is (Xj,
Yj), and the finally obtained center point is (Xn, Yn). The distance ys for shifting the comparison pattern in the y-axis direction is set so that an appropriate number (for example, about 30) of similar patterns are obtained.

Further, as shown in FIG. 5 (e), one approximate straight line L passing through (in the vicinity of) the central points (X1, Y1) to (Xn, Yn) of the maximum similar pattern is formed by using the mean square method. Required. When the angle between the obtained straight line L and the y-axis is obtained, the angle is the tire slip angle θ.

However, the direction of the rotation axis of the tire does not completely match the X-axis of the image due to an error in the mounting angle of the CCD camera and the like. Therefore, in a state where the vehicle goes straight and the slip angle is 0, the slip angle is measured in the same manner as described above, and the measured value is recorded as the slip angle reference error θ0. Straight line L
By subtracting the slip angle reference error θ0 from the angle formed between the tire slip angle θ and the y-axis, the tire slip angle θ can be obtained more accurately (FIG. 5F).

FIG. 6 is a flowchart of the above-described slip angle calculation process. CPU of slip angle calculation device 24
First, one road surface image is read (S10). Here, an image of の of the combined road surface image of FIG. 4, for example, an image of the left front wheel FL is input. Then, a reference pattern is set at the center of the input image (S12). The center point of the reference pattern is (Xi, Yi). Pattern matching between the reference pattern and the comparison target pattern is performed (S14). The center point of the first comparison target pattern is (X
min, Ymin). The similarity of the matching result is recorded in association with the pattern center point. Until the matching of the comparison target pattern whose x coordinate of the center point is Xmax is performed, that is, until the matching of the comparison target pattern at the right end of the search area is completed, the processing of S14 is repeatedly performed through the determination step of S16.

When S16 becomes no, the center point of the largest similar pattern having the largest similarity is detected and recorded from among the comparison target patterns arranged in the horizontal direction (S1).
8). Then, the y coordinate of the comparison target pattern used in S14 is compared with the area upper limit value Ymax (S2).
0). If y ≦ Ymax, a predetermined value y0 is added to the y coordinate, and the process returns to S14. Thereby, the detection of the center point of the maximum similar pattern (S14 to S18) is repeated while shifting the pattern center point stepwise by y0.

If the determination in S20 is no, pattern matching and similar pattern detection for the entire search area have been completed. Then, the process proceeds to S22, and an approximate straight line connecting the center points (X1, Y1) to (Xn, Yn) detected so far is obtained (S22). Then, the slip angle θ is calculated from the inclination of the obtained straight line with respect to the y-axis (S24).

Since the slip angle of one wheel has been obtained as described above, it is determined whether or not the calculation of the slip angle of the four wheels has been completed (S26). If the processing of the road surface image of the four wheels has not been completed yet, the process returns to S10, and the road surface image of the next wheel is read.

If it is determined in S26 that the slip angles of the four wheels have been calculated, a road surface image taken after a predetermined time is input, and the above-described processing is repeated again. As a result, the tire slip angle that changes every moment is sequentially obtained.

The preferred embodiment of the present invention has been described above. According to the present embodiment, the tire slip angle is obtained from a road surface image captured using a CCD camera. Therefore, there is no need to attach heavy objects to the wheels,
The tire slip angle can be accurately determined.

In the present embodiment, the slip angle is obtained by utilizing the fact that the flow of the road surface during the camera exposure time is reflected in the photographed image. The slip angle is obtained by using the so-called image blur in reverse. All you have to do is shoot the road with a standard camera at a shutter speed that is not too fast.

Next, a modification of this embodiment will be described.

(1) A photographing device other than a CCD camera may be used. Preferably, a camera having a solid-state imaging device (such as a MOS type) that is as small and light as the CCD camera is applied.

(2) As shown in FIG. 7, an optical fiber is attached to the wheel as image transmission means. The optical fiber is connected to a camera, which is located in the cabin or other suitable location. The road surface image is transmitted through an optical fiber and photographed by a camera. In this configuration, a relatively large camera, for example, a conventional video camera having a cathode ray tube can be applied. Further, an image transmission unit other than the optical fiber may be applied.

(3) In this embodiment, an analog video signal is output from the control unit of the CCD camera. However, it goes without saying that the digital image signal may be processed consistently throughout the entire process.

(4) The road surface image may be a color image. After converting from a color image to a grayscale image, the slip angle may be calculated.

(5) The multiviewer 18 for synthesizing the road surface images of the four wheels may be omitted. For example, the road surface image for each wheel may be recorded on a separate VTR device, and the slip angle may be determined from the recorded image.

(6) Instead of the VTR device, any other image recording device may be used. For example, it is preferable to apply a known image memory device.

(7) In the above embodiment, the slip angle was obtained from the recorded image outside the vehicle. However, the computer device may be mounted on a vehicle and the slip angle may be determined inside the vehicle. In the embodiment, the slip angle is measured for the purpose of the test. However, the slip angle may be measured for another purpose, for example, for controlling the vehicle in actual running.

(8) In the processing of FIG. 5, a search area is set in the road surface image. The shape and size of the search area are arbitrary. The entire road surface image may be a search area. The shapes and sizes of the reference pattern and the comparison target pattern may also be appropriately modified.

(9) In the above processing, the slip angle is calculated from the stripe pattern of the road flow appearing in one image. However, the slip angle may be calculated by calculating the flow on the road from a plurality of images obtained sequentially. Here, the slip angle is calculated from a moving image instead of a so-called still image.

(10) A CCD camera (or other photographing device) may be mounted on the vehicle body. In this case, a road surface image viewed from the vehicle body is captured. By performing the same processing as described above on the road surface image, the vehicle body slip angle is obtained. The vehicle body slip angle is an angle indicating a direction in which the vehicle body moves with respect to a road surface.

(11) The tire slip angle can be obtained based on the road surface image viewed from the vehicle body. The road surface is photographed by a camera attached to the vehicle body, and the wheel steering angle at the time of photographing is recorded. The wheel steering angle is an angle indicating the direction of the wheel with respect to the vehicle body. The wheel steering angle may be directly detected, or may be obtained from the steering wheel turning angle. The tire slip angle is obtained by subtracting the wheel steering angle from the vehicle body slip angle.

(12) The vehicle speed can be measured using the apparatus shown in FIG. In this case, the setting of the shutter speed is changed so that the vehicle speed can be measured favorably. For example,
The shutter speed is set very short. And
The vehicle speed is calculated from the length of the flow of the pattern in the road surface image.

(13) The tire slip angle is not limited to the definition in FIG. The slip angle may be any angle that indicates the direction in which the road surface flows with respect to the tire. The present invention is similarly applied to a tire slip angle defined based on a different standard from FIG. For example, the supplementary angle of the slip angle in FIG. 1 may be measured. Further, other parameters that can indicate the angle (eg, trigonometric functions) may be measured.
The same applies to other slip angles as well as the tire slip angle.

[0048]

As described above, according to the present invention, the slip angle can be obtained from the flow direction of the road surface in the road surface image. The road surface image can be photographed using a light-weight solid-state imaging device or the like, whereby the slip measurement can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a definition of a tire slip angle.

FIG. 2 is a block diagram illustrating a configuration of a slip angle measurement device according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing a state where a CCD camera is mounted on wheels.

4 is a diagram schematically showing an image obtained by combining road surface images taken by the four CCD cameras of FIG. 2 into one;

FIG. 5 is a diagram illustrating a process of obtaining a slip angle from a road surface image.

FIG. 6 is a flowchart illustrating a process in which a slip angle calculation device obtains a slip angle from a road surface image.

FIG. 7 is a diagram illustrating a road surface image capturing device according to a modification.

[Explanation of symbols]

10 vehicles, 12a, 12b, 12c, 12d wheels,
14a, 14b, 14c, 14d CCD camera, 20
VTR device, 24 Slip angle calculation device.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Masahiko Mizuno 41-cho, Yokomichi, Nagakute-machi, Aichi-gun, Aichi Prefecture F-term (reference) 2F065 AA32 AA37 CC11 CC12 CC13 DD02 FF04 JJ03 JJ05 JJ26 LL02 QQ17 QQ18 QQ31 QQ38 RR06 UU05 5B057 AA16 BA15 DC08 DC32

Claims (9)

[Claims] 1. A method for measuring a slip angle, comprising: taking a road surface image while traveling using a camera mounted on a vehicle; and determining a slip angle from the road surface image. 2. The slip angle measuring method according to claim 1, wherein the slip angle is determined based on the flow direction of the road surface in the road surface image by utilizing the fact that the road surface image is reflected in the road surface image during the camera exposure time. A method for measuring a slip angle, characterized in that it is determined. 3. The slip angle measurement method according to claim 2, wherein a plurality of patterns similar to each other are searched for from the road surface image, and a flow direction of the road surface is obtained from positions of the plurality of patterns. Method. 4. The slip angle measuring method according to claim 3, wherein a reference pattern is set in the road surface image, and a pattern similar to the reference pattern is searched for from the road surface image. 5. The slip angle measuring method according to claim 1, wherein a tire slip angle is obtained from a road surface image viewed from a wheel. 6. The slip angle measuring method according to claim 1, wherein the vehicle body slip angle is obtained from a road surface image viewed from the vehicle body. 7. The slip angle measuring method according to claim 1, wherein a tire slip angle is obtained from a road surface image viewed from a vehicle body and a wheel steering angle. 8. The slip angle measuring method according to claim 1, wherein a road surface image is photographed using a solid-state imaging device. 9. A slip angle measurement, comprising: photographing means mounted on a vehicle for photographing a road surface image during traveling; and slip angle calculating means for calculating a slip angle from the road surface image photographed by the photographing means. apparatus.